Obsessive-compulsive disorder (OCD) is a common psychiatric illness that affects up to 2-3% of the population. People with OCD experience anxiety-provoking, intrusive thoughts, known as obsessions, and feel compelled to perform repetitive behaviors, or compulsions. The only medications proven effective for OCD are serotonin reuptake inhibitors (SRIs), but even with SRI treatment, most patients continue to experience significant OCD symptoms, impaired functioning, and diminished quality of life. Recent evidence suggest that a different neurotransmitter, glutamate, may contribute to the symptoms in OCD. Medications that target glutamate hold promise for ameliorating symptoms for those patients continuing to suffer from OCD. In this study we are recruiting patients to receive the drug NPL-2003, which is thought to modulate the neurotransmitter glutamate, added to whatever other OCD medications they are taking in a 12-week open label study.